Utility systems usually generate, transmit,
and distribute power at a fixed frequency such as 50 or 60 Hz, while
maintaining a reasonably constant voltage at the consumer's terminal. The
consumer may use many different electronic or electrical products which
consume energy from a DC or AC power supply which converts the incoming
AC into the required form.

In the case of products or systems running on AC, the frequency may be
the same, higher, lower or variable compared to the incoming frequency.
Often, power needs to be controlled with precision. A power electronics
system interfaces between the utility system and consumer's load to satisfy
this need.

The core of most power electronic apparatus consists of a converter using
power semiconductor switching devices that works under the guidance of
control electronics. The converters can be classified as rectifier (AC-to-DC
converter), inverter ( DC-to-AC converter), DC-to-DC converter, or an AC
power controller (running at the same frequency), etc.

Often, a conversion system is a hybrid type that mixes more than one basic
conversion process. The motivation for using switching devices in a converter
is to increase conversion efficiency to a high value. In few situations
of power electronic systems, the devices (power semiconductors) are used
in the linear mode too, even though due to reasons of efficiency it’s getting
more and more limited.

Power electronics can be described as an area where anything from a few
watts to over several hundred megawatt order powers are controlled by semiconductor
control elements which consume only few microwatts to milliwatts in most
areas. As per industry estimates indicated in an editorial of Power Conversion
and Intelligent Motion Journal (2012), the power electronics industry component
in the U.S. was around US$ 60 billion, from a total estimated electronics
industry of around US$ 990 billion.

Power Conversion Electronics

Power conversion electronics can be described as a group of electrical
and electronic components arranged to form an electric circuit or group
of circuits for the purpose of modifying or controlling electric power
from one form to another.

For example, power conversion electronics is employed to provide extremely
high voltages to picture tubes to display the courses of aircraft approaching
an airport.

In another example, power conversion electronics is employed to step up
low voltage from a battery to the high voltage required by a vacuum fluorescent
display to allow paramedics to display a victim's heartbeat on a screen.
This also allows paramedics to gain information en route to the hospital,
which may save the patient's life.

Twenty years ago, power conversion was in its infancy. High efficiency
switchmode power supplies were a laboratory curiosity, not a production
line reality.

Complex control functions, such as the precision control of stepper motors
for robotics, microelectronics for implanted pacemakers, and harmonic-free
switchmode power supplies, were not economically achievable with the limited
capabilities of semiconductor components available at the time.

Importance of Power Electronics in the Modern World

At the beginning of the 20th century the world population was around
1.5 billion; by the year 2020 it’s projected to be around 7.5 billion.
Rapid technology evolution coupled with the population explosion has resulted
in an increase in average electrical power usage, from about one-half million
MW in the year 1940 to a projected eight million MW in the year 2020. This
magnitude of growth when coupled with the increasing electrical power sophistication
associated with process control, communications, consumer appliances/electronics,
information management, electrified transportation, medical, and other
applications--results in roughly 49 percent of all electrical power delivered
to user sites today being reprocessed via power electronics. This is expected
to increase to about 85 percent by the year 2020. By 2020 approximately
5.8 million MW of electrical power will be processed by power electronics.
Typical power electronics applications include electronic ballasts, high
voltage DC transmission systems, power conditioners, UPS systems, power
supplies, motor drives, power factor correction, rectifiers and, more recently,
electric vehicles. With computer systems, telecom products and a plethora
of electronic consumer appliances which require many power electronic sub-systems,
the power electronics industry has become an important topic in the electronics
industry and the information technology area.

Semiconductor Components

In modem power electronics apparatus, there are essentially two types
of semiconductor elements: the power semiconductors that can be defined
as the muscle of the equipment, and microelectronic control chips, which
provide the control and intelligence. In most situations operation of both
are digital in nature. One manipulates large power up to mega or gigawatts,
the other handles power only on the order of microwatts to milliwatts.

Until the 1970s, power semiconductor technology was based exclusively
upon bipolar devices, which were first introduced commercially in the 1950s.
The most important devices in this category were the p-i-n power rectifier,
the bipolar power transistor, and the conventional power thyristor. The
growth in the ratings of these devices was limited by the availability
of high purity silicon wafers with large wafer diameter, and their maximum
switching frequency was limited by minority carder lifetime control techniques.
In the 1980s another bipolar power device, the Gate Turn-Off Thyristor
(GTO), became commercially available with ratings suitable for very high
power applications. Its ability to turn-on and turn-off large current levels
under gate control eliminated the commutation circuits required for conventional
thyristors, thus reducing size and weight in traction applications, etc.

Although these bipolar power devices have been extensively used for power
electronic applications, a fundamental drawback that has limited their
performance is the current controlled output characteristic of the devices.
This characteristic has necessitated the implementation of high power systems
with powerful discrete control circuits, which are large in size and weight.

In the 1970s, the first power Metal-Oxide-Semiconductor Field Effect Transistors
(MOSFETS) became commercially available. Their evolution represents the
convergence of power semiconductor technology with mainstream CMOS integrated
circuit technology for the first time.

Subsequently, in the 1980s, the Insulated Gate Bipolar Transistor (IGBT)
became commercially available.

The MOSFET and IGBT require negligible steady state control power due
to their Metal-Oxide-Semiconductor (MOS) gate structure. This feature has
made them extremely convenient for power electronic applications resulting
in a rapid growth in the percentage of their market share for power transistors.

The ratings of the power MOSFET and IGBT have improved rapidly in recent
years, resulting in their overtaking the capability of bipolar power transistors.
The replacement of bipolar power transistors in power systems by these
devices that was predicted 15 years ago has now been confirmed. However,
the physics of operation of these devices limits their ability to handle
high current levels at operating voltages in excess of 2000 volts.

Consequently, for high power systems, such as traction (electric locomotives
and trams) and power distribution, bipolar power devices, namely the thyristor
and GTO, are the best commercially available components today. Although
the power ratings for these devices continue grow, the large control currents
needed to switch the GTOs has stimulated significant research around the
world aimed at the development of MOS-gated power thyristor structures
such as MOS Controlled Thyristors (MCT). The development of the insulated
gate power devices discussed above has reduced the power required for controlling
the output transistors in systems. The relatively small (less than an ampere)
currents at gate drive voltages of less than 15 volts that are needed for
these devices can be supplied by transistors that can be integrated with
CMOS digital and bipolar analog circuitry on a monolithic silicon chip.

This led to the advent of smart power technology in the 1990s.

Smart power technology provides not only the control function in systems
but also serves to provide over-current, over-voltage, and over-temperature
protection, etc. At lower power levels, it enables the implementation of
an entire sub-system on a monolithic chip. The computer-aided design tools
that are under development will play an important role in the commercialization
of smart power technology because they will determine the time-to-market
as well as the cost for development of Power Application Specific Integrated
Circuits (PASIC). Sometimes these devices are called Application Specific
Power Integrated Circuits (ASPIC). In systems such as automotive electronics
or multiplex bus networks and power supplies for computers with low operating
voltages (below 100 volts), the power MOSFET provides the best performance.
In systems such as electric trams and locomotives, the GTO is the best
commercially available component. In the near future, MOS gated thyristor
structures are likely to replace the GTO. Towards the mid-90s GaAs power
diodes have entered the marketplace providing better switching characteristics
as well as lower forward drop, etc. On a longer time frame, it’s possible
that devices based upon wide band-gap semiconductors, such as Silicon Carbide,
could replace some of these silicon devices.